Erosion resistant materials find use in many applications wherein surfaces are subject to eroding forces. For example, refinery process vessel walls and internals exposed to aggressive fluids containing hard, solid particles such as catalyst particles in various chemical and petroleum environments are subject to both erosion and corrosion. The protection of these vessels and internals against erosion and corrosion induced material degradation especially at high temperatures is a technological challenge. Refractory liners are used currently for components requiring protection against the most severe erosion and corrosion such as the inside walls of internal cyclones used to separate solid particles from fluid streams, for instance, the internal cyclones in fluid catalytic cracking units (FCCU) for separating catalyst particles from the process fluid. The state-of-the-art in erosion resistant materials are chemically bonded alumina castable refractories. These alumina castable refractories are applied to the surfaces in need of protection and upon heat curing hardens and adheres to the surface via metal-anchors or metal-reinforcements. The alumina castable refractory readily bonds to other refractory surfaces. The typical chemical composition of one commercially available chemically bonded alumina castable refractory is 80.0% Al2O3, 7.2% SiO2, 1.0% Fe2O3, 4.8% MgO/CaO, 4.5% P2O5 in wt %. The life span of the state-of-the-art refractory liners is significantly limited by excessive mechanical attrition of the liner from the high velocity solid particle impingement, mechanical cracking and spallation. Therefore there is a need for materials with superior erosion and corrosion resistance properties for high temperature applications. The cermet compositions of the instant invention satisfy this need.
Ceramic-metal composites are called cermets. Cermets of adequate chemical stability suitably designed for high hardness and fracture toughness can provide an order of magnitude higher erosion resistance over refractory materials known in the art. Cermets generally comprise a ceramic phase and a binder phase and are commonly produced using powder metallurgy techniques where metal and ceramic powders are mixed, pressed and sintered at high temperatures to form dense compacts.
The present invention includes new and improved cermet compositions.
The present invention also includes cermet compositions suitable for use at high temperatures.
Additionally, the present invention includes an improved method for protecting metal surfaces against erosion and corrosion under high temperature conditions.
These and other objects will become apparent from the detailed description which follows.